mRNA levels of MIP-1β (CCL4) and MCP-2 (CCL8) in the lungs of C3H/HeN, BALB/c, and C57BL/6N mice after mycoplasma infection. At 3, 14, and 28 days after infection, lungs were collected, and total RNA was isolated. MIP-1β (CCL4) (a) and MCP-2 (CCL8) (b) transcript levels were measured by using real-time RT-PCR. The levels of mRNA were standardized to the β-actin housekeeping gene. The vertical bars represent the means ± the SEM (n = 6 for each time point and mouse strain) of the fold difference in MIP-1β (CCL4) and MCP-2 (CCL8) mRNA levels, relative to the average baseline values of samples from uninfected (control, inoculated with mycoplasma broth medium) mice. An asterisk denotes a statistical difference (P ≤ 0.05) compared to uninfected mice of the same mouse strain.